In order to develop effective strategies for preventing drug use and related problems, it is critical that factors playing a causal role in drug use be identified. Of particular interest are causal factors that are malleable and potential targets of intervention. Etiologic risk factors can be most effectively identified using longitudinal studies of children, who are passing through the period of high risk for initiation of drug use. In this longitudinal research, it is necessary to consider drug use outcomes as they occur through different developmental stages. For example, drinking a beer is more normative for a high school senior than it is for a 10 year old child. In addition, factors that are protective in childhood might not be protective later in adolescence. For this reason, the Etiology Branch is involved in a longitudinal study of an epidemiologically defined sample of urban children. Data from this study will enable the identification of factors that play a causal role in the onset of early drug use and subsequent problems related to use of psychoactive substances as they develop through childhood and adolescence. Current research is addressing the role of parenting behavior, in particular parent monitoring and supervision of a child's activities, in relation to early drug sampling and later more problematic drug use. Future research will investigate the role of neighborhood factors in the development of drug use and will examine the potential causal and mediating effects of peer drug use and level of antisocial behavior in relation to other risk factors at different stages of drug use and different points in the life span. In addition, another project is currently underway that employs a multistage sampling design to assess the comorbidity between drug use and depression. The combination of longitudinal follow-up of this epidemiologic sample with more intensive measures administered on a screened subset of this sample will enable a more thorough understanding of drug use and both its causes and consequences.